Biomaterials for orbital fractures repair.

The unique and complex anatomy of the orbit requires significant contouring of the implants to restore the proper anatomy. Fractures of the orbital region have an incidence of 10-25% from total facial fractures and the most common age group was the third decade of life. The majority of cases require reconstruction of the orbital floor to support the globe position and restore the shape of the orbit. The reason for this is that the bony walls are comminuted and/or bone fragments are missing. Therefore, the reconstruction of missing bone is important rather than reducing bone fragments. This can be accomplished using various materials. There is hardly any anatomic region in the human body that is so controversial in terms of appropriate material used for fracture repair: nonresorbable versus resorbable, autogenous/allogenous/xenogenous versus alloplastic material, non-prebent versus preformed (anatomical) plates, standard versus custom-made plates, nonporous versus porous material, non-coated versus coated plates. Thus, the importance of material used for reconstruction becomes more challenging for the ophthalmologist and the oral and maxillofacial surgeon.


Introduction
Fractures of the orbital region has an incidence of 10-25% from total facial fractures [1] and the most common age group was the third decade of life (29%) [2]. The most common etiology seems to be violent assault or nonviolent traumatic injury (49.4%) [2] and the most frequent fracture involved the zygoma (23.6%), followed by the orbital floor (21.4%), maxilla, mandible and nasal bones [3]. For these patients modern imaging analysis offers a unique chance to quantitatively asses the surgical result and stability over the time. This can provide valuable information for future recommendation [4]. Careful assessment of the defect size should be performed preoperatively with the CT scan in the sagittal view which is in the course of the orbital nerve, plus the coronal view [5].
Jaquiéry differentiated between the following classes in orbital trauma [6]: Class I: Small, isolated defects of the orbital floor or the medial orbital wall of approx. 1 -2 cm 2 Class II: Defects of the orbital floor and/or the medial orbital wall > 2 cm 2 , bony structures of the medial wall of the infraorbital fissure are intact.
Class III: Defects of the orbital floor and/or the medial orbital wall > 2 cm 2 , without bony structures of the infraorbital fissure.
Class IV: Defects of the whole orbital floor and the medial wall to the infraorbital fissure. The timing of surgery has also been debated over the years. Except in the circumstance of a trapdoor fracture with the potential for an ischemic contracture of the entrapped tissue, generally is allowed several days for orbital and eyelid edema to resolve. This delay also allows more accurate assessment of extraocular muscle function [7].
As demonstrated by studies, there is lack of consensus in recognizing one material as the optimal one for orbital reconstruction. Available products are: 1. Titanium meshes presents a series of advantages [8], [9]. In 2009 Scollozzi revealed in his paper a high rate of success with an acceptable rate of major clinical complications (10%) and an anatomic restoration of the bony orbital contour and volume that closely approximates that of the contralateral uninjured orbit. [ • Not radiopaque (not visible on postoperative images) • Lack of rigidity when a very thin wafer of PPE is used. When a thicker rigid wafer is used there is a risk of causing a dystopia. • Less drainage from the orbit than with titanium mesh 4. Composite of porous polyethylene and titanium mesh By combining titanium mesh with porous polyethylene the material becomes radiopaque and more rigid than porous polyethylene of a similar thickness. Some surgeons also believe that there is less risk of having retained sharp barbs, which can lead to an entrapment of soft tissues during placement [13]. Advantages: • Availability • Stability • Contouring (eased by the artificial sterile skull) • Adequate in large three-wall fractures (the pre-bent plate is limited to medial wall and orbital wall fractures only).
• Radio-opacity • No donor site needed • Tissue incorporation may occur Disadvantages: • Less drainage from the orbit than with titanium mesh 5. Resorbablematerials :Thermoplastic and non-thermoplastic materials Thermoplastic blends of cornstarch material with ethylene vinyl alcohol copolimers reinforced with hydroxyapatite were used based on their mechanical properties and their modulus closed to that of human bone [14]. Advantages: • Availability • Handling/contourability (only for thermoplastics) • Smooth surface and smooth edges Disadvantages: • No radio-opacity • Degradation of material with possible contour loss • Sterile infection / inflammatory response • Difficult to shape according to patients anatomy (only for non-thermoplastics) • Less drainage from the orbit than with uncovered titanium mesh (in case when non-perforated material is used) 6. Preformed orbital implant: Bittermann shows that using computer-assisted techniques, anatomically preformed orbital implants and intraoperative imaging the surgeon can have precise and predictable results of orbital reconstructions [15]. Advantages: • Radio-opacity • Smooth surface • Minimal or no contouring necessary Disadvantages: • Cost The first step in a choice for an implant is to focus on its most important features in order to reduce complications incidence.
These features should be: light weight, porosity (the implant must allow vascular orbital tissues to invade its structure), biocompatibility (the implant has to be tolerated and accepted by the orbital tissues), low rate complications, easy to insert, economic cost. ( Table 1) illustrates factors influencing the decision for the implant choice. Table 1 Factors influencing decision for the choice of the material Surgeon experience Severity of fracture Individual characteristics Cost The multitude materials with different results in published studies show that we don't have the answer for the best type of implant for orbital reconstruction. With the increasing need to develop clean, non-toxic and environmentally friendly techniques, hydroxyapatite powders have been extracted using bioproducts from marine sources (e.g. coral, cuttlefish shells), animal teeth and bones (porcine, bovine), natural gypsum or natural calcite [16,17]. Compared with hydroxyapatite produced by synthetic methods, hydroxyapatite generated partially or entirely from biogenic sources is supposed to be accepted better by the living organisms, because of its physic-chemical similarity to the human bone apatite.